WASHINGTON - As the Senate returns from recess this week, Sen. Chuck Schumer, D-N.Y., said he thinks the bi-partisan Gang of Eight will have its immigration plan completed by the end of the week.

"We hope that we can have a bipartisan agreement among the eight of us on comprehensive immigration reform by the end of the week," Schumer said today on CBS' "Face the Nation." "Over the last two weeks, we've made great progress. There have been kerfuffles along the way, but each one of those, thus far, has been settled."

Schumer said that the staffs of each Gang of Eight member has worked 12 hours a day to fine-tune the details of their immigration plan and reach an agreement on every issue.

In an interview on NBC's "Meet the Press," Sen. Lindsey Graham, R-S.C., also a member of the Gang of Eight, set a longer time frame of a "couple of weeks" before the plan is completed.

But one Republican member of the bi-partisan group has expressed concern that the deal on immigration reform is being reached in haste.

Sen. Marco Rubio, R-Fla., has called for more hearings and time to review the plan in order to encourage "healthy public debate."

"Arriving at a final product will require it to be properly submitted for the American people's consideration, through the other 92 senators from 43 states that weren't part of this initial drafting process," Rubio said in a statement last week. "In order to succeed, this process cannot be rushed or done in secret."

Sen. John McCain, R-Ariz., disputed the idea that the plan is being rushed, saying on CBS' "Face the Nation," "I reject this notion that something is being railroaded through. This is the beginning of the process, not the end of it."

Graham defended Rubio, even though questions have been raised about whether he will ultimately agree to a bi-partisan plan.

"Marco Rubio has been a game changer in my party," Graham said. "He will be there only if the Democrats will embrace a guest worker program and a merit-based immigration system to replace the broken one and we'll regain our sovereignty by securing our borders and having control of jobs through E-Verify. Marco will be there."